Pascale Rudolph

Femtosecond pulse laser processing of TiN on silicon

Ultrashort pulse laser microstructuring (pulse duration 130 fs, wavelength 800 nm, repetition rate 2 Hz) of titanium nitride (TiN) films on silicon substrates was performed in air using the direct focusing technique. The lateral and vertical precision of laser ablation was evaluated. The TiN ablation threshold changed with the number of pulses applied to the surface due to an incubation effect. An ablation depth per pulse below the penetration depth of light was observed. Columnar structures were formed in the silicon substrate after drilling through the TiN layer.

Laser interaction with coated collagen and cellulose fibre composites: fundamentals of laser cleaning of ancient parchment manuscripts and paper

Laser cleaning of delicate biological composite materials such as ancient parchment manuscripts from the 15th and 16th century and printed paper from the 19th century is demonstrated with an ultraviolet excimer pulsed laser at 308 nm. Laser fluence levels must stay below the ablation and destruction threshold of the parchment or paper substrate, and have to surpass the threshold of the contaminant matter. Foreign layers to be removed must exhibit a higher optical density than the artifact substrates. Synthetic carbonaceous dirt modelled by water-soluble black crayons showed a characteristically weak featureless laser-induced plasma spectroscopy spectrum near the noise limit. It turned out that laser-induced plasma spectroscopy is of limited use in monitoring halting points (or etch-stops) because it relies on the destruction not only of the laterally inhomogenously distributed contaminant but also of pigment phases on a microscopically rough parchment substrate. Laser-induced fluorescence spectroscopy, however, promises to be a valuable non-destructive testing technique for etch-stop monitoring.

Physical chemistry of the femtosecond and nanosecond laser–material interaction with SiC and a SiC–TiC–TiB2 composite ceramic compound

The interaction of nanosecond laser pulses in the ultraviolet wavelength range and femtosecond laser pulses in the near-infrared region with the semiconductor SiC and the composite compound SiC–TiC–TiB2 was investigated. Surface analytical techniques, such as XPS, depth profile (DP), and micro-Raman spectroscopy (μ-RS) were used to identify the chemical changes between untreated and laser-treated areas. Single-pulse irradiation led to material modifications in the condensed state in most instances. Multi-pulse results differed depending on the pulse duration. Crystal structure changes were observed as a consequence of laser-induced melting and resolidification. In air contact all components underwent oxidation reactions according to thermodynamic expectations. Exceptions were observed under exclusion of oxygen, SiC was reduced to elemental Si.

Near-UV laser interaction with contaminants and pigments on parchment: laser cleaning diagnostics by SE-microscopy, VIS-, and IR-spectroscopy

Abstract Potentials and limitations of the near-UV pulsed laser cleaning of parchment (wavelength 308 nm, pulse duration 17 ns) are demonstrated by the application of scanning electron microscopy (SEM), colour metrics and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) at model contamination/pigment/parchment systems. Pigment-binder systems stable and unstable against near-UV laser treatment could be identified. A chemical degradation threshold fluence of a goat parchment model substrate was determined which practically coincided with its ablation threshold fluence. This indicates that the fluence range of destructionless laser cleaning at 308 nm is almost not impaired by chemical modfications below the ablation limit. Nevertheless, spectroscopic diagnostics are necessary to guarantee destructionless cleaning for practical cases where the chemical conversion threshold fluence deviates from the ablation threshold to lower values.

Laser Cleaning Investigations of Paper Models and Original Objects with Nd:YAG and KrF Laser Systems

Conventional cleaning methods (mechanical, wet) are not always sufficient for the restoration of brittle papers, fissures and sensitive inscriptions. Partial cleaning of paper in the vicinity of sensitive media, such as water-colour, is particularly difficult because of the lack of precision using conventional techniques. In these cases, where high spatial accuracy and localized treatments is necessary, laser cleaning might promise to be an additional tool for conservators.

Near-Ultraviolet Pulsed Laser Interaction with Contaminants and Pigments on Parchment: Spectroscopic Diagnostics for Laser Cleaning Safety

Laser cleaning is a contactless and dry process. The absence of chemical agents, spectroscopic selectivity, micro-precision, computer-aided handling, and the combination with in-situ diagnostic techniques makes it attractive not only for industrial but also for parchment and paper restoration applications. Potentials and limitations of the near-UV pulsed laser cleaning of historical parchment manuscripts (λ = 308 nm, τ = 17 ns) have been investigated by experiments at contamination/pigment/parchment model systems. Major attention is being payed to spectroscopic diagnostics which allow quantification of laser-induced degradation reactions, and thus support the cleaning safety. First results by diffuse reflection absorption FT-IR microscopy, spectrophotometry, colour metrics, laser-induced fluorescence and plasma spectroscopy are presented.

Laser Cleaning of Pressure Sensitive Tapes on Paper

Cleaning of paper objects can be very complex due to various combinations of contaminants. Conventional chemical and mechanical cleaning methods suffer from the common phenomenon that the foreign matter is diluted into the substrate rather than removed. In these cases, and where high spatial accuracy and localized treatments is necessary, laser cleaning promises to be an additional tool for conservators.